Units of computing systems and other electronic products are often mounted in rack enclosures to achieve a dense vertical stacking. The racks are often standardized at 19 inches or 23 inches of front panel width, have standard mounting hole positions, and provide areas for connecting interface cables and power to the units in the rack. The units may be interconnected to work together or may be independent and only in the same rack because of available space and power connections.
Input power for units in a rack may be standard AC (alternating current) power but may also be from one or more power converting units that provide power for some or all of the units in the rack, i.e., load units. The power converting units often provide functions such as redundant inputs and provide a DC (direct current) output. Providing isolation from primary input power, input redundancy, and power conversion to a regulated DC voltage in a separate power unit allows the other load units in the rack to be smaller and more efficient since they do not need their own power supplies to perform those functions. When a power converting unit is incorporated in a rack or otherwise used to provide power for a group of load units, there is a need for communication between the load units and the power converting unit to ensure reliable operation of the load units. It is within this context that the present invention arises.